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Plant Biomass Estimation Using Dielectric Properties

Plant Biomass Estimation Using Dielectric Properties. 2006 Annual International Meeting Portland, Oregon July 9 - 12 Paper Number: 063092. C. L. Jones Asst. Professor , ASAE member N. O. Maness Professor - Horticulture M. L. Stone Regents’ Professor, ASAE Fellow

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Plant Biomass Estimation Using Dielectric Properties

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  1. Plant Biomass Estimation Using Dielectric Properties 2006 Annual International Meeting Portland, Oregon July 9 - 12 Paper Number: 063092 C. L. Jones Asst. Professor , ASAE member N. O. Maness Professor - Horticulture M. L. Stone Regents’ Professor, ASAE Fellow J. B. Solie Sarkey’s Professor, ASAE Fellow G. Brusewitz Professor Emeritus, ASAE Fellow

  2. Motivation for Estimating Biomass • Chemical application decisions • Yield prediction • Grazing management Paper Number: 063092

  3. Plant Biomass Estimation Using Dielectric Properties Answer the following: • Using a free-space system, can electromagnetic response (300 to 900 kHz range) be used to detect volumetric moisture of spinach? • Using this system, what is the optimum frequency within this range for detecting volumetric moisture of spinach in situ? • What is the relationship between the electromagnetic transmission attenuation and moisture content (biomass) of spinach plants? Paper Number: 063092

  4. Background Dielectric properties… • measure of polarizability when subjected to electric field (Von Hippel, 1954) • Represented by relative complex permittivity • ε = ε′ - jε″ • ε′ …material’s ability to store energy (dielectric constant) • ε′ = C·C0-1 (capacitance of system with and without sample) (Sacilik et al., 2006) • ε″…material’s ability to dissipate energy Paper Number: 063092

  5. Background Influential factors… • Water: influential factor due to polar nature • Bulk density • Frequency • Temperature • Chemical composition • Permanent dipole moment association between water and constituent molecules (Nelson, Nelson and Stetson, Von Hippel) Paper Number: 063092

  6. Background Free water (non-bound) • ε = ε′ - jε″ = ε∞ + (εs - ε∞ )(1 + iωt)-1(Debye, Hasted) • ε∞: permittivity at high frequencies…no polarization • εs : permittivity at zero frequency • t: relaxation time, ω: radian frequency (2pf) • Biomaterial contains both bound and free water • Dielectric properties of bound water: between ice and free water depending on how tightly water is bound Paper Number: 063092

  7. Background Biomaterials (free and bound water) • ε = ε′ - jε″ = ε∞ + (εs - ε∞ )(1 + iωt)-ά(Cole-Cole Equation) • ά = breadth of time constant distribution (single relaxation = 1, infinitely broad distribution = 0) • Dependent on temperature, pressure and chemistry Paper Number: 063092

  8. Background Testing biomaterials • Potential difference measurements of elements of known permittivity...compare to test material(ex: water ε′ = 80) • OR…correlation of transmission potential difference between 2+ quantities of sample material with gravimetrically determined water content of samples (Berbert et al, Boldor et al, Jorgensen et al, Kim et al, Kraszewski, Nelson, Lawrence, Noh, Stetson, Sokhansanj, Trabelsi….) Paper Number: 063092

  9. Background • Area of investigation • 300 to 900 khz • Minimize the Maxwell-Wagner effect (Kittel) • Reduced interaction with plant geometry (1 km - 333 m wavelength) • Radiofrequency spectrum AM radio - 535 kilohertz to 1.7 megahertz Paper Number: 063092

  10. System Design Equivalent Circuit Paper Number: 063092

  11. System Design Electrostatic Free-Space System • Parallel aluminum plates (sizes tested in FEMLAB) • 12.7 cm x 12.7 cm x 0.32 cm - and - 30.5 cm x 30.5 cm x 0.32 cm • Sensed volume: 0.6 m x 1 m x 1m • Vector Network Analyzer (VNA): Agilent 8712ET Paper Number: 063092

  12. Preliminary Known Sample Testing • Response of system with known quantities of water • Measured signal attenuation modulus K = 10log10(P0Pz-1) where: P0 = incident power Pz = power at receiving antenna • Ksample = Ktest - Kspace Paper Number: 063092

  13. Known Sample Response 30.5 cm plates 12.7 cm plates Paper Number: 063092

  14. Frequency Selection Example Determining frequency – known water samples Paper Number: 063092

  15. Response to Plant Material • Flat of healthy spinach presented to system on plastic holder • Randomly chosen samples harvested, weighed, and placed in oven for moisture content analysis • With all vegetation removed, attenuation was recorded of the empty flat Paper Number: 063092

  16. Response to Plant Material Greenhouse-grown spinach, 12.7 cm antennae Paper Number: 063092

  17. Response to Plant Material Greenhouse-grown spinach, 30.5 cm antennae Paper Number: 063092

  18. Characteristic Curve with Plant Material(30.5 cm antennae) • R2 was equal to linear relationship, 0.95 • Curve appeared linear Paper Number: 063092

  19. Influence of Extraneous Material • Tested with plant material samples • Placed at lower limit of sensing area Paper Number: 063092

  20. Predicting Water Content and Biomass(30.5 cm antennae) Paper Number: 063092

  21. Conclusions • Electromagnetic Free-space System shows promise for estimating water content in situ (biomass in homogenous samples) • 450 to 500 kHz is appropriate Paper Number: 063092

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